Default firewall rules are still here.
http://forum.mikrotik.com/t/buying-rb1100ahx4-dude-edition-questions-about-firewall/148996/4
drop-all-at-the-end should only be put in the input chain.
It is obvious that the router must allow everything between the entire LAN and the external WAN, otherwise why did you put a router and connect to the internet?
The last rule of the forward chain is used to drop everything that comes from the WAN, but that has not been requested (NATted) by the internal LAN.
Following too many suggestions only leads to confusion.
The things @jaclaz wrote were just a test to make you understand, they were not rules to leave, and then add the rule to allow PCs in LAN to use the internet.